I've always of the frame of mind that Lois is stunningly attractive. Considering her upbringing and being a tomboy, you'll still more often than not see her as business casual, she's not often glitzed up to the max, and even when not she's still smokin. But when she does its a whole other level. Why I feel this way...its just the way she always seemed to be portrayed to me in my day in the comics. For example I remember one issue shortly after Superman came back to life where Lex held some party, and Lois shows up glammed up with a new haircut and dress and even Jimmy's mouth literally falls to the floor.
As for Superman, pretty much your prototypical ruggedly handsome heartthrob. That is, when he's not in his public Clark guise, in which he purposely makes himself as inconspicuous as possible. But even for all that women still notice that Clark is handsome, if not a little nerdy. Again why I feel this way is just because its pretty much the way he was always portrayed to me when I was growing up (well except the public Clark Kent exceptions, as not even that existed back then, as the edict was cool Clark).